This invention relates to a flexible joint used for joining constituent units of culverts or covered conduits such as waterworks, gully drains, subways and tunnels.
Known in the art is a flexible joint for a culvert as shown in FIG. 10. This prior art flexible joint includes a pair of annular connecting members b, b' which are fixed to opposed end surfaces of two adjacnet culvert units a, a' to be connected together. These connecting members b, b' have inner annular walls b1, b1' and outer annular walls b2, b2' and space is defined between these annular walls b1 and b2, and b1' and b2'. A plurality of bearing bars c disposed circumferentially at a predetermined interval have their end portions received in the spaces in the connecting members b, b' in a manner to be slidable in the axial direction of the culvert within a certain limited range in the spaces of the connecting members b, b' and yet to be prevented from disengaging from the connecting members b, b'. There are provided a first outer flexible sealing member d and a second outer flexible sealing member e of a generally short cylindrical configuration with undulating surfaces which are made of rubber or a synthetic resin and are disposed radially outwardly of the circumferentially arranged bearing bars c and have thier end portions fixed to the inner annular walls b1, b1' of the connecting members b, b'. There is also provided an inner flexible sealing member f of a generally short cylindrical configuration having undulating surfaces which is disposed radially inwardly of the bearing bars c and has thier end portions fixed to the inner annular walls b1, b1' of the connecting members b, b'. The inner annular walls b1, b1' of the connecting members b, b' thus are hermetically connected to each other by the flexible sealing members d, e and f.
In constructing a culvert by a shield driving method, a primary lining is constructed by connecting segments g, g' one after another and a secondry lining is constructed by moving a slide form machine stepwisely by a predetermined distance to deposit raw concrete under a high pressure to the peripheral surface of the completed first covering. For constructing a frame of the flexible joint which enables depositing of raw concrete in the secondary lining, annular frame plates h, h' for the secondary lining are fixed to the radially inner end portions of the annular inner walls b1, b1' of the connecting members b, b'. Further, annular anchor receiving plates i, i' are fixed to the radially inner end portions of these frame plates h, h'. Hook portions of a plurality of anchor members j, j' arranged circumferentially are hooked in holes formed in the anchor receiving plates i, i' and the other end of the anchor members j, j' are spot-welded to the radially inner end portions of the outer annular walls b2, b2' of the connecting members b, b'. The annular frame plates h, h' are divided in plural portions in the circumferential direction and adjacent ones of these portions are connected to each other by means of bolts screwed to joint plates k, k.
In the above described process, raw concrete is deposited by the slide form machine up to points blocked by the frame plates h, h' to perform the second covering work. In FIG. 10, reference character m designates a inside cover made of rubber provided for providing an inside peripheral portion of the flexible joint which is flush with the inner peripheral surface of the other portions of the culvert units a, a' and also for preventing intrusion of dust into the space between the frame plates h, h'. Reference character n desigantes a skin plate provided for preventing intrusion of dust into the space abvove the first flexible sealing member d.
In this type of flexible joint for a culvert, if there is a relatively large gap between respective adjacent bearing members c which are arranged circumferentially, there will arise a case where, when water is caused to leak into the space outside of the second flexible sealing member e, the second flexible sealing member e is deformed by pressure applied by the leaking water to project radially inwardly into the gap between the bearing bars c. This projecting portion of the second flexible sealing member e which is located between the adjacent bearing bars c tends to be clamped by these bearing bars c and thereby damaged when the culverts a, a' move toward each other due to a change in the underground environment such as earthquake. For preventing such damage, the bearing bars c have been arranged in such a manner that the gap between respective adjacnet bearing bars c is made as small as possible or even nil. Such arrangement of the bearing bars c, however, requires a large number of the bearing bars c which results in excessive strength of the bearing bars c which is quite unnecessary for supporting the second flexible sealing member e and increase in the total weight of the bearing bars C. Thus, difficulty arises in assembling the flexible joint and the manufacturing cost of the flexible joint also increases.
Further, in this type of prior art flexible joint, there may arise a case where, after use of the flexible joint for many years, the space between the inner annular walls b1, b1' of the connecting members b, b' radially outwardly of the second flexible sealing member 2e is filled with leaking water. In this case, the flexible sealing member e is supported by the bearing bars c against pressure of the leaking water and this state will continue so long as the joint maintains the initial state of installation. When the culvert units a, a' move toward each other due to an earthquake in this state, no problem will arise if water flows out through the gap of the skin plate n which is spot-welded at one end thereof only to either of the connecting members b, b'. When, however, water does not flow out of the inside space of the joint for the reason that the earth outside of the joint has only a small coefficient of water permeability or that the outside of the joint is filled with concrete, water filled in the space between the connecting members b, b' is compressed and water pressure increases sharply. This causes the bearing bars c to be pressed through the flexible sealing member e with the result that the flexible sealing member e and the bearing bars c will be deformed and ultimately damaged.
Furthermore, in the prior art flexible joint shown in FIG. 10, the frame including the frame plates h, h' is constructed for depositing concrete for the secondary lining as described above. This frame projects from the primary lining ( segments g, g') into the culvert space by a large measure and this prevents an easy shift of the slide form machine. Besides, since the standard distance of movement for a single operation of the slide form machine is 9 m, in a case where the flexible joint is located in a middle position within this distance of movement, the operation for depositing concrete is stopped halfway at the location of the frame plate (e.g., frame plate h) before reaching the standard distance and then the slide form machine is carried to the other side of the flexible joint and the operation for depositing concrete is resumed to deposite concrete to the location of the other frame plate (e.g., frame plate h'). Thus, in this case, the operation for depositing concrete cannot be made in a single operation but it must be performed in two separate operations and this decreases the efficiency of the secondary lining.
The secondary lining is performed by depositing concrete by a predetermined thickness in the radial direction measured from the wall surface of the culvert formed by the shield driving. In the priro art flexible joint shown in FIG. 10, allowance of variation in this thickness in the radial direction in the flexible joint section caused by irregularity in the digging work is an extremely small value of D1. Therefore, when the flexible joint has fallen inwardly beyond the value D1 due to irregularity caused during the digging work, the slide form machine abuts against the inner end portion of the frame and thereby is prevented from further executing the planned secondary lining. Accordingly, a very high accuracy in the shield driving work is required for maintaining this small allowance of variation D1.
It is, therefore, a first object of the present invention to provide a flexible joint for a culvert which is light in weight, easy to handle and of a low manufacturing cost.
It is a second object of the invention to provide a flexible joint for a culvert which, when the joint is subjected to an abrupt deformation due to an earthquake or other reason in a state where the space between the connecting members radially outside of the second flexible sealing member is filled with leaking water, is capable of preventing deformation and damage of the elements of the flexible joint due to increase in the water pressure.
It is a third object of the invention to provide a flexible joint for a culvert capable of improving the efficiency of the secondary lining and reducing the required accuracy of the shield driving.